Study On Structure And Properties Of Doped SnO2Semiconductor Solid Solution Electrodes

SnO2is one of important semiconductor materials with wide band gap. It has been applied extensively in many fields such as electrode materials, optical devices due to the unique electric and optical properties of modified SnO2system by doping. The first-principles calculation based on density function theory have been used to investigate the relationship between microscopic structure and macroscopic properties of SnO2electrode materials, providing a new way of designing and researching electrode materials.In the paper, physical and chemical properties of rutile SnO2electrode material before and after doping have been completely studied. The differences between them were discussed and the reasons for the property variations also were presented. The main research contents were as following:(1) The models of pure SnO2and doped-SnO2systems via metals Ti, Bi and Mn as well as rare earth elements La, Ce, Pr and Nd were built up;(2) The microscopic properties containing structural characteristics, valence bond forms, band structures, electronic state densities, difference charge densities of them have been calculated and analyzed systematically;(3) Compared with the micro-and macro-property variations before and after doping, we discussed the main causes of the property variations;(4) The electrode material SnO2doped with Pr, as one representative, was characterized by means of SEM, XRD and CV and so on. Its structural variations, surface morphology and conductive mechanism have been discussed on the basis of the analysis results.All the results show:(1) The lattice parameters of Ti doped SnO2system exhibit an approximate linear decline trend with the increase of Ti doping concentration. SnO2is still direct band gap semiconductor after doping Ti, the value of which gradually decreases with Ti doping concentration increasing. The covalent feature of Ti-O bond is stronger than Sn-O bond. However, the formation energy of the Sn1-xTixO2solid solution firstly increase and then descend with the increasing of Ti doping concentration up to x=0.5, obtaining a minimum value of-6.11eV, which shows the Sno.5Ti0.5O2solid solution is the largest stable form in the Sni_xTixO2system.(2) The lattice parameters of Bi doped SnO2system show an approximate linear increase trend with the increase of Hi doping concentration. An impurity level, formed by Bi6s states, intersects with the Fermi energy, which results in that Bi doped SnO2system has half metal property. The ionic feature of Bi-O bond is stronger than Sn-O bond. When doping ratio of Bi and Sn is0.0625, the formation energy of the Bi doped SnO2system achieves the minimum value of-10.28eV, obtaining the most stable structure. With the increase of doping ratio, the formation energy gradually increases and the stability decreases. (3) The lattice parameters of Mn doped SnO2system exhibit an approximate linear decline trend with the increase of Ti doping concentration. The conduction band bottom of SnO2appears deep impurity level after Mn doping. The band gap of Sn0.75Mn0.25O2is0.62eV, smaller than pure SnO2, which indicates that the electrical conductibility can be enhanced by doping Mn. The covalent characteristic is more than Sn-O bond. However, Sn0.5Mn0.5O2has the most stable structure owing to the minimum formation energy of-1.94eV in the Mn doped SnO2system.(4) After rare earth elements doping, the unit cell of SnO2is distorted and the bulk of it expands obviously. The band gaps of La or Ce doped SnO2system increases after doping, while ones of Pr or Nd doped SnO2system on the contrary. After doping Ce, Pr or Nd, the conduction band bottom of SnO2is introduced acceptor level. At the same time, some impurity levels appear the valance band top for Pr or Nd doped SnO2system, forming the donor levels, which increases the probabilities of electron excitation and the conductibility of SnO2to some extent.(5) The lattice parameters of (?) doped SnO2system exhibit an approximate linear increase trend with the increase of Pr doping concentration. The band gap decreases and the conductibility of SnO2increases after doping Pr because of the interaction between the impurity Pr f level and Fermi energy. When doping ratio of Pr and Sn is0.0625, the formation energy of Pr doped SnO2system obtains the minimum value of-15.59eV, achieving the most stable structure. With the increase of doping ratio, the formation energy gradually increases and the stability decreases. The corresponding experiment exhibits that the particles of SnO2become small and the arrangement is close-grained after Pr doping. In the lower doping ratio, electrode life is longer than blank electrode. The life of Sn0.9375Mn0.062502electrode as one representative achieves the maximum time of121h, and the catalytic degradation rate of phenol was50%after2h, which demonstrates that Sn0.9375Mn0.062502electrode has excellent stability and electrochemical catalytic degradation phenol performance.